50 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
show distinctly the arrangement in more than one layer 
noted above (see fig. 10). The entire ventral surface is 
now covered with large ectoderm cells, and there is a con- 
tinuous layer of test all over the body. With the excep- 
tion of the small dorsal nerve cord (7.s.), the branchial 
sac or pharynx is the only organ inside the ectoderm. It 
is roughly of triangular form with a ciliated pad projecting 
inwards from each of its sides. The two lateral pads are 
the peripharyngeal bands and the third is a median ventral 
ridge (the hypopharyngeal) which shortly becomes con- 
verted into a ciliated groove leading forward to the 
endostyle. Six or seven sections further on (Pl. IV. fig. 1) 
this ventral ciliated area is seen as a shallow groove, two 
sections in front of that (Pl. IV. fig. 2) it has become a 
deeper, narrower groove, and in another couple of sections 
it forms, along with the peripharyngeal grooves (p.p.) 
which have now moved down ventrally and coalesced 
with it, the sloping lateral edges of the aperture of the 
endostyle into the branchial sac (Pl. IV. fig. 3). 
The posterior end of the endostyle is found about section 
220. Pl. IV. fig. 1, ex., shows its appearance in section 
223 where it is composed of a mass of glandular cells lying 
half-way between the ventral surface of the branchial sac 
and the ectoderm, and having no connection with the 
pharynx. In section 225 (Pl. IV. fig. 2) the endostyle is 
larger and has a central lumen around which the glandular 
cells are placed ; it has now nearly come into connection 
with the deep hypopharyngeal groove. In another couple 
of sections we find this connection established as is shown 
in section 228 (Pl. IV. fig. 8) where the endostyle has a 
considerable cavity opening by a narrow slit into the 
ventral part of the pharynx. The glandular cells are not 
equally developed around the whole wall of the endostyle 
‘but are arranged in four definite longitudinal tracts. After 
